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Abstract
A reversible phase transformation between icosahedral and rhombohedral approximant structures has been studied by T.E.M. The microcrystalline rhombohedral phase, stable at low temperature, transforms into an icosahedral phase via an intermediate pentagonal structure. The icosahedral phase, metastable at low temperature, transforms between 500 and 675[ddot]C into the rhombohedral phase via different transient states: modulated icosahedral phases and pentagonal approximants. These intermediate states have been interpreted in the hyper-space description as resulting of shear phason waves, propagating in the perpendicular space. It has to be noticed that chemical composition variations associated to these shear waves and predicted by the theory have been experimentally observed.
